A strengthened platinum material having good high-temperature strength properties has conventionally been used as a structural material for handling a glass or ceramic material in a molten state. The strengthened platinum material for use in melting the glass material or the like at high temperature is required to have high so-called creep strength. In producing such a strengthened platinum material, the preparation of a material particularly having a prolonged durability time until a creep rupture is an important challenge.
This strengthened platinum material is required to have, for example, high creep strength at 1,400° C. as high temperature strength properties. Control of material structure is therefore very important in the production of the strengthened platinum material. A method for finely and uniformly dispersing a metal oxide such as zirconium oxide in a platinum base metal of the strengthened platinum material has conventionally been known for improving the high creep strength, and various production methods have been proposed to obtain the strengthened platinum material in which such a metal oxide is dispersed.
As one of the examples, Japanese Patent Application Laid-Open No. 8-134511 relates to a method for producing a strengthened platinum material in which a metal oxide is finely dispersed in a platinum base, and discloses that after a platinum alloy consisting of a metal element as a precursor for the metal oxide and platinum is melt-sprayed, the resultant platinum alloy powder is subjected to wet-milling.
According to the production method, a strengthened platinum material can be obtained, in which the production time is shortened; blisters do not occur in production steps such as compression molding, heat treatment, hot forging, annealing, and cold rolling; and which has stable creep strength. The strengthened platinum material according to the production method, however, sometimes produced fine blisters on the surface of the material upon heat treatment at a high temperature of 1,400° C.
The occurrence of fine blisters on the surface of the material at high-temperature heat treatment of the strengthened platinum material obtained by the production method according to the Japanese Patent Application Laid-Open No. 8-134511 is estimated due to the release at the high-temperature heat treatment of the gas adsorbed to the surface of fine powders when the melt-sprayed platinum alloy powder is subjected to wet-milling. In order to prevent fine blisters at the high-temperature heat treatment, it is contemplated to carry out subsequent production treatment steps at high temperatures, thereby minimizing the gas adsorbed to the platinum alloy fine powder.
Meanwhile, Japanese Patent Application Laid-Open No. 2000-160268 discloses a method, in which a platinum alloy including 0.05 to 2% by weight of zirconium, samarium or the like is milled by an atomizing process, oxidized and sintered for 1 to 100 hours at a high temperature of 1,400 to 1,750° C., and then subjected to plastic working. The Japanese Patent Application further describes that when the platinum alloy powder is oxidized and sintered at a high temperature of 1,400° C. or higher, metal oxide particles such as zirconium oxide dispersed in the strengthened platinum alloy material are dispersed in a state having a relatively large diameter of about 1 to 10 μm.
According to the production method, although an easily deformed strengthened platinum material may be achieved, the material can only maintain its creep properties at a high temperature of 1,000° C. or higher at a certain level, and creep properties at even higher temperatures tend to drop compared with the case of fine metal oxide particles. That is to say, when the temperature for subsequent production treatment processes are simply raised to high temperatures, in order to remove the gas adsorbed to a wet-milled platinum alloy fine powder in the production method according to the Japanese Patent Application Laid-Open No. 8-134511, it is estimated that the particle size of the metal oxide will be increased, which causes reduction of the high-temperature creep properties.